On Start Engine Revs to Infinity and does not idle

trentdoubledown11

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1984
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Just a quick update. I plugged all the ports. Replaced the worst of the hoses. I adjusted idle screws and idle mixing screws to be most restrictive. I have the throttle and choke mechanisms moving pretty good and do not seem to stick when manually operated.

Other than getting the engine to backfire, the revving issue persists.

I even tried setting up the vacuums to match the diagram (and plugging where parts are missing). Same result.

I did notice what looks like burnt fuel on the underside of the air cleaner lid. When I tried the old air cleaner, it did a wonderful dance atop the carb for a few seconds (shorter stud didn't let me secure the old one back). The fuel gauge is also moving towards empty.

I went ahead and ordered a new carb and will put that in this afternoon. I've had a suspicion that the carb was the culprit the whole time so I want to see if I am right.
 

DoubleDingo

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Keep us posted on how this turns out
 

WesN

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The choke brake/choke pull/ secondary air valve vacuum pot at the passenger rear corner is bent way over and I am guessing the carb at some time has been dropped on that corner while off the motor. Beside it not working properly there is possibly other issues from being dropped. Engine off open the secondary air valve and look down inside with a light to see if the throttle blades are closed or possibly bent. Also engine off hold open the choke and open the throttle and release the choke fast idle cam should drop down it is the tab/weight thing inside of the electric choke. Either could cause it to rev. All could be from a drop.
 

DoubleDingo

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Carb'ed Vortec 350; 1972 L48 350
The choke brake/choke pull/ secondary air valve vacuum pot at the passenger rear corner is bent way over and I am guessing the carb at some time has been dropped on that corner while off the motor. Beside it not working properly there is possibly other issues from being dropped. Engine off open the secondary air valve and look down inside with a light to see if the throttle blades are closed or possibly bent. Also engine off hold open the choke and open the throttle and release the choke fast idle cam should drop down it is the tab/weight thing inside of the electric choke. Either could cause it to rev. All could be from a drop.

It'll be easy to check all of this when he removes the carb to replace it. If has been dropped, that is most likely the issue.
 

trentdoubledown11

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C10
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305
Yeah that pull was bent intentionally when were troubleshooting. We could see where it was rubbing the outside of the carb and bent it out for clearance (probably too much).

After taking the carb off the cause of the revving was really obvious. The spring on the driver side was installed upside down and was preventing closure. When we were manually pulling on the throttle it looked like it was working but it had another half turn to go to close up.

So final diagnosis, user error. :)

I found an Edelbrock 1406 on sale at NAPA so I put that one on. I like it a little better so far because all the adjustment screws are much easier to get to. I'm still considering rebuilding the previous one and putting it back though.

Original Carb with that spring:

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Trouble Carb without that sprig:
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The bright side of all this is that after 5 years of sitting, my grandfather's truck is finally running. I still have some adjustments to linkages and I want to tighten up the steering but he is that much closer to getting back on the road.

I just now realized I didn't take a photo of under the hood after the carb replacement.

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83Burban

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@trentdoubledown11.

Glad you got it firgured out.

Lol the whole time was reading through this thread...."throttle return spring" was all I could think. Had this problem on my buddies 80' Stingray. It had just rusted through and broke.

But....a couple months ago I had my nearly 20' long 1969' Lincoln Continental parked in the garage swapping to an eddy carb....and I just simply forgot to reconnect the spring. Funny thing is the car had idled for about 30min with no issue while I set the idle screws. When I got in, put it in reverse, and tapped the throttle.....well....that was absolutely f****** terrifying.

So as im standing on the break smoking the tires in reverse...car slowly sliding back and forth....ladies car to the left, garage wall on the right, my 83 Burban kinda behind me .....full panic mode..... It took me a second to come to the conclusion that "I need to turn off the car off".

Now....do you know where the key is located on on 60s vintage Lincoln's? Under the dash and pretty well in the middle of the car. Man....i don't think I could have pooped out a jelly bean at that moment. Moral of the story.....ALLWAYS DOUBLE CHECK THE THROTTLE RETURN. LOL
 

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